Building your own gold drywasher for desert prospecting can be very fun, and once you know how they wok, very easy.
The first thing you need to do is decide what kind of drywasher you are going to make. If this is your first time building one, then I suggest you build a simple hand-powered bellows model. They are the simplest and cheapest to make, and can easily be modified to electric or gas power in the future.
Basically, there are three main parts to a drywasher: the hopper, the riffle board, and the bellows. I assume that you already know what a drywasher is and how it works so I wont go into great detail on each part’s function.
When choosing what kind of hopper you want, it’s important to consider your situation. If you are going to be prospecting alone, you should consider building a large, box hopper. That way, you can fill up a full hopper, then sit down and process the material, rather than stop every few shovel fulls. If you are working with a partner, or your machine is automated, you can keep shoveling on dirt without ever having to stop to pump the bellows, so you don’t need a large hopper. If this is your situation, then all you need is a frame with a scree and a bag to direct the dirt onto the riffle board.
The riffle board is a very important piece. It is situated under the hopper, and all the material passes over it. The riffle board of a drywasher consists of four parts: the top frame where the riffles are, some kind of porous cloth under that, a screen to support the cloth, and on the bottom is another frame with supports for each riffle. The frames are then screwed together to sandwich the cloth and screen together between them. A good cloth to use is unbleached muslin. The riffles can be made of wood or steal. It is also important that the bottom frame extends past the riffles a little bit to create a dead air space behind each one.
Next is the bellows. The bellows is on the very bottom of the machine, and the riffle board sits on top of it. It is important that the whole thing is airtight. A good material to use is canvas. Also, the bottom needs to have one or more holes in it covered in slabs of rubber to act as a valve to let air in, but not out.
Now you have to figure out how to make the bellows pump. Swamp cooler parts make good mechanics. A pulley for a crank, and a threaded rod with a plate at the end attached to some pivoting arms connected to the bottom of the bellows works well.
Once you have all the parts made, all there’s left to do is put it all together. There are many ways you can do this, but make sure the material from the hopper will fall on the back end of the riffle board. Even more important is the angle of the riffle board. It should be at a sharp enough angle that the material can make its way off of the edge of the board and onto the ground, but not so sharp that the material simply falls of. Now just bolt the pieces to four legs and you have yourself a drywasher!
These are not meant to be exact plans, but rather a guideline. What I would suggest doing is look at as many pictures of drywashers as you can find for inspiration. Once you have an idea of what you want to make, just refer back to this article as a guide, and get Building!